Asphaltic cement



United States Patent Cfiice 3,094,427 Patented June 18, 1963 3,094,427 ASPHALTIC CEMENT Philip C. Doyle, Rocky River, Edwin 0. Hook, Chagrin Falls, and Harley F. Hardman, Lyndhnrst, Ohio, assignors to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Filed Dec. 30, 1960, Ser. No. 79,510 5 Claims. (Cl. 106-273) This invention relates to an improved asphalt cement for paving purposes. More particularly, this invention relates to a method of improving the thermal stability of an asphalt cement to retard the loss of ductile characteristics which normally occurs during high temperature mixing with aggregate in a mix mill so as to improve the service behavior of an asphaltic pavement in which said asphalt cement is incorporated.

Good ductility is recognized by those skilled in the art as an important and desirable property for an asphalt cement intended for paving purposes. It is believed that the ductility of an asphalt cement is related to the actual service behavior of an .asphaltic pavement in which it is incorporated so that as a qualitative matter the better the ductile characteristics of the asphalt cement present in the asphaltic pavement, the better will be the service behavior of the pavement.

In a paper entitled Cracking Characteristics of Asphalt Cement, which appears in volume 27 of the Proceedings of the Association of Asphalt Paving Technologists, at page 581, the author, Philip C. Doyle, who is a co-inventor of the present invention, proposes that the ductile characteristics of asphalt cement are meaningful with respect to the tendency of an asphaltic pavement in which it is incorporated to fracture or crack in service, particularly if the ductile characteristics of the asphalt are measured on a ductilometer at lower temperatures and speeds than those commonly employed. The author reports tests on core samples which were drilled from pavements actually in service, showing both good and bad resistance to surface cracking. It was found from these various tests that when the ductile characteristics of the asphalt cement recovered from these core samples were run at 55 F. and l cm./min. speeds on the ductilometer the ductility values of the asphalt cement could be closely correlated with the service behavior of the pavement. By comparison, it was found that when the ductility of the recovered asphalt was determined at temperatures of 77 F. and at speeds of 5 cm./min. the ductility values obtained were not always consistent with field results with respect to the cracking tendency of the pavement. Besides showing that ductility measurements of the asphalt cement at 55 F. and l cm./min. speed on the ductilometer offers a convenient means for predicting the service behavior of an asphaltic pavement with respect to surface cracking, these results reported for these low temperature ductility measurements stress the importance of preserving good ductile characteristics in the asphalt in order to insure that the asphaltic pavement will provide good service behavior.

It has been found that asphalt cements generally have initially good ductile characteristics so that if this high degree of ductility were possessed by the asphalt after being laid into a pavement, good service behavior of the pavement could be expected. However, it is well known that the ductility of the asphalt cement is materially lost during the high temperature mixing of the asphalt cement with aggregate so that the ductile characteristics of the asphalt cement in the pavement is usually of a relatively low value. For example, a typical asphalt for paving having a penetration value of 70 to 85 measured at 77 F. obtained from a Mississippi-Arkansas-Illinois crude had a ductility of 150+ centimeters (cms.) when measured on a ductilometer at 55 F., 1 cm. speed. This asphalt, however, after being mixed with gravel aggregate in a standard mix mill at 310 F. in accordance with conventional trade practices showed a ductility value of only 10 cms. when measured at 55 F. and 1 cm. speed.

This, of course, demonstrates the drastic effect the high temperature mixing has on the ductile characteristics of an asphalt cement. It is believed that the loss in ductile characteristics which occurs during the mixing operation is due primarily to an oxidation mechanism induced by the high temperatures that must be employed. It is to be understood, however, that the present invention is not at all dependent upon what mechanism is responsible for this loss in ductile value since the fact remains that such a loss does occur. There is, of course, some progressive hardening and loss of ductility in the laying of the asphalt and in its exposure to the elements while present in the pavement, but this loss is negligible in relation to the loss which occurs during the mixing operation. Consequently, if some way is found to inhibit the loss occurring during the mixing operation, the ductile characteristics of the asphalt can be largely preserved and the pavement in which it is incorporated will have greater resistance to cracking.

Generally, the degree of ductility loss in the mixing operation increases with the increase of temperature and/or time employed in mixing and the time the finished mixture is held in a truck at the mixing temperature prior to its actual laying. According to good trade practices, the temperature at which a mix mill is operated is generally selected as the temperature which will give seconds viscosity on a Saybolt-Furol viscometer for the particular asphalt that is used. It is believed that this temperature provides the best film thickness of asphalt on the aggregate for paving purposes. However, since few mix mills are equipped with thermocouples, the operating temperature in actual practice of these mills has .a tendency to vary over wide limits and the problem of the loss of ductile characteristics in the asphalt cement becomes particularly aggravated. Also, since the location of these hot mix paving plants are frequently dist-ant from the paving job, it often happens during cold climatic conditions that the asphalt must be mixed at much higher temperatures than the proper mixing temperature in order that the paving mix will arrive at the job at a sufiicient temperature for paving. Moreover, frequently the time of mixing is not carefully or uniforrnly controlled at the mix mill with commensurate depreciation of the ductile characteristics of the asphalt cement. In addition to these operational variables which may unduly deteriorate the ductile value, asphalt cements vary in their sensitivity to change in the high tempenature mixing operation. Some asphalt cements therefore are much more sensitive than others depending on the crude oil from which they are produced and the method of manufacture. It will be obvious that many asphalt cements which have high heat susceptibility are definitely destroyed by the mixing operation when the mixing is carried out at excessive temperatures or at proper mixing temperatures but for excessive mixing periods.

The primary object of the present invention, therefore, is to minimize the loss of ductile characteristics in an asphalt cement which occurs during the high temperature mixing with aggregate so as to improve the asphalts resistance to cracking in the pavement. It is a further purpose of this invention to permit much greater latitude in the time and temperature of mixing of asphalt with aggregate. A still further object of this invention is to permit asphalt cements which are originally borderline with respect to ductile characteristics to be be employed.

These objects and other objects which will become apparent from the following discussion may be accomplished in accordance with the present invention by adding to the asphalt cement before the mixing operation a boron-containing chemical agent. The boron compound for use in the invention is to be selected from the group consisting of:

(I) Tri-(tetrahydrofurfuryl) borate. This compound may be readily prepared by reacting 3 moles of tetrahydrofurfuryl alcohol with 1 mole of H BO with mild heating under conditions in which the water of reaction is removed from the reaction mixture as it is formed;

(II) Di-[4-(oleoyloxyethyl)-4-azaheptanediol-2,6] diborate having the following formula:

The above compound may be'readily prepared by reacting oleoyl chloride with fl 'hydroxyethyl di-isopropanol amine to form a fatty acid ester amine which is then reacted with boricwacid under conditions in which the water of reaction is removed from the reaction mixture as it is formed.

(In) A material which is a mixture of compounds of the following general formula:

where R is an alkyl radical containing from 9 to 11 carbon atoms. This material is prepared by reacting 2 moles of tri-(di-isopropylcarbinyloxy)-boroxine with 1 mole of a mixture of tertiary alkyl primary amines wherein two substituents of the tertiary carbon atom are methyl radicals and the third substituent is R as defined above. This mixture of t-alkyl primary :amines is available from Rohm & Haas Company under the trademark Primene 81R, having a molecular Weight range of from 185 to 213 and a neutral equivalent number of 191. The reaction is conducted under conditions so that the 2 moles of di-isopropanol formed during the reactionis removed. This material is identified in Tables A and B hereinafter as Compound III; and

(IV) Glycol borates having the formula:

where R is an a or ,8 alkylene radical having from 4 to 8 carbon atoms.

Compounds illustrative of the later class of compounds are di-(2-methylpentanediol-2,4) diborate having the formula:

di-(butanediol-1,3) borate having the formula:

a CH-O tri-(butanediol-l,3) diborate having the formula:

t-ri-(2-ethylhexanediol-l,3) diborate having the formula:

one or a mixture of the foregoing boron-containing compounds must be used. Actually, there is no upper limit but amounts over 2% by weight usually cannot be justified economically. A preferred range for the boron compound or compounds is generally from 0.01% by Weight to 0.5% by weight.

The boron compound may be introduced to the asphalt cement at some convenient point before the asphalt is charged to the mix mill employing any suitable mixing means which will insure that the additive is evenly distributed throughout the asphalt. It is very desirable to add the boron compound into the asphalt at the refinery while it is handled at elevated temperatures prior to loading for delivery. This may be accomplished in a heated tank utilizing a high-speed agitator as a mixing means.

The asphalt ingredient of this invention may be any natural or manufactured bituminous material which may be mixed with any of the common aggregates, such as crushed limestone, slag, crushed rock, sand, gravel, etc. to form an asphaltic concrete for paving. The desirable properties for such an asphalt cement may be found in highway specification manuals or in Abrahams text Asphalt and Allied Substances. In general, asphalt cement for paving purposes is required to meet penetration specifications and the preferred penetration will usually be from 50-200 at 77 F.

In preparing, an asphaltic concrete for paving, the asphalt cement of the invention is mixed with aggregate in the proportion of from 4 to 8 parts by weight of asphalt to 96 to 92 parts by weight of aggregate at a temperature in the range of from 280 F. to 350 F., but preferably the temperature will be selected, as indicated before to give seconds viscosity (Saybolt-Furol) for the asphalt cement employed.

A better understanding of the present invention will be gained from the following discussion of Oven Weather Tests comparing the loss of ductile characteristics during mixing with aggregate of an untreated asphalt cement with the same asphalt treated with boron-containing compounds of the invention.

The FOven Weather Test simulates the high temperature mixing in a conventional mix mill and correlates therewith. Results from this test have indicated that ductile characteristics measured on a sample of asphalt cement recovered from the hot paving mix prepared and heated in accordance with this test at 55 F., 1 cm. speed, parallel closely the ductile characteristics when measured at 55 F., 1 cm. speed, for a sample of the same asphalt cement recovered from a hot paving mix just before it is laid as a pavement following mixing in a conventional mix mill at the proper temperature to give 120 seconds viscosity (Saybolt-Furol) for the asphalt employed and including an average of approximately one hour transportation of the hot mixture to the job site.

In executing the Oven Test, 3000 grams of standard Ottawa sand is mixed with 120 grams of asphalt cement for two minutes at the temperature which gives 120 seconds viscosity as determined by means of a Saybolt-Furol viscometer for the asphalt cement of the test. Immediately after this mixing, the mixture is spread to a uniform depth in shallow aluminum pans measuring approximately 5 /2" in diameter and in depth and allowed to cool to room temperature. These pans containing an asphaltic mixture are then placed in an oven for exactly one hour again at the temperature which gives 120 seconds viscosity for the asphalt being tested. The pans are then removed from the oven and allowed to cool to room temperature for at least one hour. The rasphaltic mixture is scraped from the pans, placed in a rotarex, and the asphalt is recovered by extraction with benzene in accordance with Absons Method and Test which is recorded in detail beginning at page 48 of the Association of Asphalt Paving Technologists Proceedings for 1952, vol. 21. The original asphalt and the recovered asphalt on evaporation of the benzene are tested for ductility according to ASTM designation D 11344 at 55i0.9 F. and at a rate of speed of 1 cm./min. The result reported for this test is the number of centimeters the sample specimen will extend before pulling apart.

A first series of runs using the Oven Weather Test was conducted for an asphalt cement obtained from a Mississippi-Arkansas crude mixture to illustrate the effect of the use of a small amount of the boron compounds of the invention is reducing the loss in ductile characteristics in said asphalt. The boron compound for each run was added to the asphalt cement while the asphalt was maintained in a molten and mobile condition. A mechanical stirrer was provided to insure that the boron compound was evenly dispersed throughout the asphalt. The results of this series of runs is reported in Table A below:

A second series of runs employing the Oven Weather Test was conducted on an untreated and boron treated asphalt cement which is inherently less susceptible to loss in ductile characteristics during high temperature mixing with aggregate. This asphalt is produced from an Illinois crude and has a penetration of 85-100 at 77 F. The

testing procedures employed for this series of runs were the same as before and the results are reported in Table B below.

It is obvious from these data that even though the asphalt cement in itself shows fair resistance to loss in ductile characteristics during oven weathering, the treatment of this asphalt with the boron compounds of the invention is effective in further minimizing this loss.

In order to confirm the effects of the compounds of the invention as illustrated by the tests and data reported hereinbefore, an actual field test was conducted on the high temperature mixing of an asphalt cement with aggregate in a conventional mix mill where in one run the asphalt cement was treated with a boron compound of the invention and in a second run the asphalt was untreated. The asphalt cement was produced from an Illinois-Mississippi-Arkansas crude mixture and had an -100 penetration at 77 F. The asphalt in each run was mixed with crushed limestone in the same proportion using identical procedures and the same mixing temperature of 315 F. Samples of asphalt were obtained before and immediately after the mixing operation to measure the loss of ductility in each case. The asphalt sample after mixing was obtained from a sample of the hot mix by extracting with benzene in accordance with Absons Method and Test referred to hereinbefore. The ductility of the asphalt samples was measured at 45 F., 1 cm. speed on the The above data illustrate the beneficial effect of treating the asphalt with the boron compound.

It is to be understood that various modifications of the foregoing invention will occur to those skilled in the art upon reading the above description. All such modifications are intended to be included as may be reasonably covered by the appended claims.

We claim:

1. An asphalt cement for paving, having a penetration of from 50 to 200 at 77 F., and exhibiting improved resistance to the loss of ductility due to the high temperature mixing with aggregate to form a paving mix, said asphalt containing at least 0.001% by weight of a boroncontaining compound selected from the group consisting of (I) tri-(tetrahydrofurfuryl) borate, (II) di-[4-(oleoy1- oxyethyl)-4-azaheptanediol-2,6] diborate, (III) a compound of the following general formula:

where R is an alkyl radical containing from 9 to 11 carbon atoms, and (IV) glycol borates having the formula:

and where R is an alkylene radical having from 4 to 8 carbon atoms.

2. An asphalt cement'for paving exhibiting improved resistance to the loss of ductility which contains at least 0.001% by weight of a boron compound having the formula:

R \BOX where X is selected from the group consisting of o o -B/ R, -ROB R,andROH and where R is an alkylene radical having from 4 to 8' carbon atoms.

3. An asphalt cement for paving exhibiting improved resistance tothe loss of ductility which contains at least 0.001% by weight di-(2-methylpentanediol-2,4) diborate.

4. An asphalt cement for paving exhibiting improved resistance to the loss of ductility which contains at least 0.001% by weight tri-(2-ethyll1exanediol-1,3) diborate.

5. A method for preparing an asphaltic concrete for" paving consisting of the steps of adding to an asphalt" cement having a penetration of from 50 to 200 at 77 F.-

at least 0.001% by weight of a boron compound selected from the. group consisting-30f (I) tri(tetrahydrofurfury1) borate, (II) di-[4-(oleoyloxyethyl)-4-azaheptanediol-2,6] diborate, (III) a compound of the following general formula:

where R is an alkyl radical containing from 9 to 11 carbon atoms, and (IV) glycol borates having the formula:

R BO-X where X is selected from the group consisting of O O -B R, ROB R, and ROH and where R is an alkylene radical having from 4 to 8 carbon atoms, and mixing from 4 to 8 parts by Weight of said asphalt cement containing said boron-containing compound with from 96 to 92 parts by Weight of aggregate at a temperature of from 280 to 350 F. whereby the loss of ductility of the asphalt cement during the mixing with aggregate is minimized.

References Cited in the file of this patent UNITED STATES PATENTS 2,375,117 Lentz May 1, 1945 

1. AN ASPHALT CEMENT FOR PAVING, HAVING A PENETRATION OF FROM 50 TO 200 AT 77* F., AND EXHIBITING IMPROVED RESISTANCE TO THE LOSS OF DUCTILITY DUE TO THE HIGH TEMPERATURE MIXING WITH AGGREGATE TO FORM A PAVING MIX SAID ASPHALT CONTAINING AT LEAST 0.001% BY WEIGHT OF A BORONCONTAINING COMPOUND SELECTED FROM THE GROUP CONSISTING OF (I) TRI(TETRAHYDROFURFURYL), BORATE, (II) DI 4-(OLEOYLOXYETHYL)-4-AZAHEPTANEDIOL-2,6! DIBORATE, (III) A COMPOUND OF THE FOLLOWING GENERAL FORMULA: 